Infrared photography – Gale E Spring

Gale E Spring is an Adjunct A/Professor of Biomedical and Forensic Photography at RMIT University, School of Science. Melbourne. Contributor & Editor: Danielle Edwards a photographer and Director of Communications with the BioCommunications Association.

Sir Frederick William Herschel (1738-1822) first discovered infrared (IR) radiation in 1800. It took over 100 years before infrared film was realized and not until 1910 before Robert Williams Wood (1868–1955) made the first images using infrared radiation.

Infrared photography became popular in the 1930’s when the film became commercially available.

Introduction to infrared

When we speak of ‘light’, we mean the part of the visible spectrum (400 – 700 nanometres) that allows us to see. This ranges from deep blue violet, through green, yellow, orange to red and deep red. We can see all these colours and their combinations. When we have a mixture of red, green and blue light, we see ‘white light’. But visible light is just a very small portion of the electromagnetic spectrum that spans from gamma radiation to radio waves.

Beyond our human vision lies the ultraviolet (below 400 nanometres) and infrared (above 700 nanometres). These wavelengths exhibit no colour that we can see, but we have created photographic films as well as digital and electronic sensors that are sensitive to these invisible wavelengths and, therefore, we can create images using these ‘invisible’ radiations. 

We can capture images with the appropriate equipment in the ultraviolet from about 200 to 399 nanometres. Infrared film can capture an image from about 700 to 900[1] nanometres. Digital camera sensors extend this to about 1100 nanometres. This extended infrared range has made digital technology the best and only option to make images beyond what might be called ‘extended red’. 

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Reflected infrared

Materials absorb, reflect, or transmit radiation whether it is infrared (IR) or visible light. It does so in a proportion so we can capture tonality using film or sensors. Our eyes can’t see infrared, so photography using infrared capture is a surprise when we see the results. 

Infrared reflectance is what we traditionally photograph. Materials react in different ways depending on the wavelengths of light striking them. This is also true regarding the variation in wavelengths within what we generically call ‘near infrared’, i.e., 700 to 1100 nanometres. 

For example, the IR reflectance may be creating a different effect at 1100 nanometres and above, but we will not record it since it’s outside the sensitivity of film/sensor. The more infrared that is reflected off a material, the more energy strikes the film/sensor and the lighter the tonality on the print (just like photons on photographic film).

Sources of infrared

Typical sources of infrared radiation are the sun, incandescent lamps (lamps that produce heat) and electronic flash. This means the best conditions to photograph scenes or subject in the infrared are in bright sun or under hot lamps. Infrared is invisible to the human eye, so it is difficult for us to determine if there is enough IR to make an image.

In daylight, the amount of infrared will vary with time of day and weather conditions affected by clouds or overcast sky. Ironically, the best time to shoot IR is the worst time for traditional film photography. Bright, sunny, contrasty conditions usually produce good landscapes; however, rules are meant to be broken so testing and experimenting is advised. There is less infrared in shadows if you are shooting outdoors. This is similar to the fact there is less visible light in the shadows as well, but this is what produces tonality in traditional photography.

If shooting indoors, use electronic flash, tungsten or incandescent lamps. They produce a large quantity of infrared radiation. You can also use LED lamps that are designed to emit IR. Not all LED’s emit IR so check the lamp specifications. Infrared LED lamps are often used for ‘invisible’ light sources for surveillance cameras. They are also used for reversing cameras on many vehicles.

Electronic flash is a great source of infrared. It is portable and emits large quantities of light as well as infrared. Manufacturers have almost eliminated ultraviolet from flashes because it affects colour reproduction in colour film photography. Infrared, on the other hand, does not affect the colour balance in film photography since standard photographic films are not sensitive to infrared radiation. However, digital cameras are extremely sensitive to infrared radiation. Digital camera manufacturers place very effective IR absorbing filters in front of their CCD or CMOS sensors to eliminate the adverse effects of IR. Digital camera, infrared conversions, primarily remove the IR absorbing filter and replace it with a visible black/IR pass filter.

Most photographers consider electronic flash as a ‘cool’ light source. They are used when you do not wish to heat a subject under hot tungsten sources. Electronic flash does, however, emit heat, but for a very short duration. You can confirm this by placing your hand in close contact with the flash head of a small portable unit and firing the flash. You will feel a short burst of heat as the flash fires. Do not try this with a powerful electronic flash – it will cause burns.Infrared photography has no colour[2], so colour balancing is not necessary. You can set your digital camera white balance to anything you wish since it will not affect the quality of your final image. The digital camera will create a colour bias to your original image, so you will need to digitally process it to remove this cast. 

Never use fluorescent lamps for infrared photography since they produce no infrared radiation. Their lack of infrared is why they are referred to as a ‘cold light’ source.

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Film for infrared photography

Black and white infrared films

In the 1960’s, colour infrared became commercially popular as Kodak Aerochrome III Infrared Film in 35-millimeter format. Kodak ceased the manufacture of monochrome infrared film, HIE-135-36, in 2007.  This was the last film manufactured that was truly a benchmark for monochrome infrared photography.

Digital photography has re-kindled an interest in infrared. Digital cameras are inherently sensitive to infrared radiation and some cameras are easily converted to exploit their sensitivity in this range. There are many Internet sites that are devoted to film and digital infrared photography.  There has also been a resurgence of ‘false colour’ infrared using a combination of traditional filters and digital manipulation.

Silver-based, infrared films are becoming popular again as an alternative process or technique. Rollei is one film manufacturer who makes an extended Red/Infrared film available in multi formats including 35mm, 120 and 4 x 5 sheet film. 

Infrared films are sensitive to ultraviolet radiation, the visible spectrum as well as infrared radiation. To produce only the effect of the infrared exposure, you must use a filter over the lens or sensor to eliminate light that would overpower the infrared-only image.

Films in today’s market do not extend as far into the infrared as older infrared emulsions. Ilford SFX, for example, only quote up to 720 nanometres sensitivity. These films are more accurately called ‘extended red’ since they do not extend very far into the infrared. They do, however, produce interesting results even with their limited infrared sensitivity. When Kodak stopped production of their High Speed Infrared film, HIE-136-36 in 2007, the last of the 900 nanometre sensitive film was gone. One reason why Kodak stopped manufacturing this film was the extensive production difficulties in producing a quality 900 nanometre IR film.

Some films like Efke IR820 (formerly Maco[3]) and Rollei[4] have sensitivity up to 820 nanometres. 

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Storage and handling of infrared film are important. The manufacturer will usually recommend storage in a cool, dry environment or possibly refrigeration. Infrared film emulsions are not as forgiving as traditional films for storage conditions or use past their expiry date. It is best to purchase, shoot and process the film as soon as possible. Once the film is processed, the negatives can be treated and stored like any other negative material. 

All infrared film is always loaded into the camera in total darkness, even if stored in a 35mm film canister, as infrared leaks around the felt light trap on 35mm film canisters. If you are shooting 4×5-inch film, check that your film holder does not leak infrared. Some early plastic film holders leaked infrared but were quite adequate for standard black and white or colour films.

Filters for infrared photography

When making an infrared exposure you must eliminate white light. This is done with special filters that absorb all visible light but pass invisible infrared radiation.

The traditional filters manufactured by Kodak were the Wratten 87, 88 and 89 series of filters. These are no longer manufactured so other companies have filled the void with their equivalents such as the B+W IR092 and IR093. Other IR filters are also available from a variety of manufacturers and used Wratten filters can still be found. 

In early classic infrared film photography, the Wratten 25 (red) or 29 (deep red) were used since they allowed viewing through the lens while eliminating a large quantity of light (primarily blue and green). These filters can still be used today with film or digital cameras. Since red is still in the visible spectrum, you will be getting a combination of a visible red and infrared exposure.

If you want to create a photograph using only infrared radiation, you must choose a filter that blocks all visible light, including deep red. If any visible or deep red leaks through the filter, your tonal reproduction will not represent pure infrared.

Cameras for infrared photography

Film cameras

Most film cameras can be used for infrared photography.35mm and medium format film cameras can be used for infrared photography. One important consideration is the material making the shutter. Some older cameras from the 1960’s used rubberized fabric for the shutter curtain. The Miranda is an example of a camera that used a rubberized shutter curtain and will not work with infrared film. Most of these rubberized curtains leaked infrared radiation even when they were new.

Metal shutter blades are preferred for infrared photography. The Nikon F and many other cameras has all metal shutters.

Another consideration is the construction of the camera back. Some 35mm and medium format cameras had a window made of red plastic so the film type on the canister or the frame number could be read in the light. This plastic window leaks infrared.  Covering the window with metalized tape solves this problem. 

Large format cameras have a bellows between the lens and the film to keep light out of the camera. All large format photographers are aware that bellows can leak light through pinholes or cracks and cause the film to fog. Many large format photographers, however, are not aware bellows can be made of materials that leak infrared radiation although they may work perfectly well in visible light. Only testing will indicate whether the bellow is acceptable for infrared photography. By putting a piece of infrared film in the camera, placing the camera in the sun for a few minutes and processing the (hopefully) unexposed film, you can tell whether the bellows will work with infrared films.

Another large format consideration is wood construction can leak infrared radiation. Wooden cameras are not recommended for use with infrared films, however, depending on their construction, they may leak very slowly. If you intend to use a wooden camera, you must test it first and leave it in the sun long enough so the test mimics real time use.

Digital cameras

All digital sensors are sensitive to infrared radiation. Camera manufacturers install a filter (hot mirror) over the sensor to absorb unwanted infrared and assist in colour correction of the sensor. For general digital photography, infrared is a seen as a problem that affects exposure and colour. Over the years of digital sensor development, infrared absorbing filters have become more efficient. This means early models of digital cameras usually allow more infrared radiation to ‘leak’ through the filter and reach the sensor. This makes them more desirable for infrared photography without any conversion to the camera. 

IR Conversions for DSLR and mirrorless cameras

A modern digital camera can be converted to an infrared camera by removing the manufacturer’s infrared absorption filter located just in front of the sensor and replacing it with a special filter that blocks visible light but passes infrared radiation. The photographer can still see through the viewfinder of a single-lens-reflex (SLR) or mirrorless camera for focusing and composition since the visibly opaque filter is only over the sensor. When the shutter opens, the infrared image passes through the filter, striking the sensor to produce the image. Infrared has no colour, any colour formed in the image you see is simply an artefact of the digital camera sensor. There are various ways to neutralise the colour bias, including post-processing.

Infrared does not focus in the same plane as ‘white’ light. A focus adjustment will be made in digital camera conversions to compensate for this chromatic focus shift. But infrared focus shift is also dependent on the lens characteristics as well as the focal length. Unless a specific lens is always used, the focus adjustment to the camera must be a compromise. It is recommended that the photographer always shoot at a smaller aperture to assist in depth-of-field to compensate for slight focus shift. 

Camera conversions are a delicate operation and should always be done by specialist camera repair facilities. The cost in 2023 can range from $400.00 to $600.00.

Lenses for infrared photography (film and digital)

Manufacturers of lenses concentrate their optical quality at wavelengths in the visible range of 400 to 700 nanometres. This quality includes the ability of the lens to focus all colours creating the image at the same image plane. Chromatic aberration is the failure of the lens to focus all colours at the same image plane. Chromatic aberration is a bigger problem with telephoto lenses since the light must travel longer in the lens and can deviate more over the greater distance. Wide-angle lenses do not usually suffer chromatic aberration; therefore, you will find apochromatic lenses are only available in longer focal lengths.

All glass lenses transmit infrared. The infrared image, however, is not usually focused in the same plane as image made by white light. If you focus the white light image through the ground glass or viewfinder, the projected infrared image (that you can’t see) at the film/sensor plane will be out of focus. The use of a digital camera Live View or mirrorless technology assists in focusing directly through the view finder.

Some lenses have a red mark engraved on the barrel to indicate an infrared focus shift. Once focused in white light, adjusting the focus to the red mark may help as well. Most are not accurate and should only be considered a guide.

Apochromatic lenses do a better job keeping focus in the same plane in the infrared since they are chromatically corrected for visible wavelengths and extend somewhat into the infrared and ultraviolet. Although they are not specifically corrected for wavelengths in the infrared, they work better than standard, non-apochromatic lenses. 

A recommended way to optimize focus is to use a smaller aperture to increase depth of field and compensate for the focus shift. Testing will be necessary to see if the red indicator is correct. Make your tests at a wider aperture so depth of field is minimized, and you can critically determine sharp focus. Most lenses will focus fine in the IR if you can just locate the IR focal plane.Since lenses are optimised for visible light, some lenses may create internal reflection that can cause hot spots to appear in the image with infrared radiation. As the number of lens elements increase, the likelihood of internal reflections also increases.  The problem seems to occur more with complex 35mm lenses and is rarely seen in large format lenses.

How much infrared is there?

One of the biggest problems shooting infrared if determining proper exposure. With digital infrared, you can get an immediate indication of exposure. Shooting infrared film has always been a challenge since you don’t know the results until its processed.

The issue is that you can’t ‘see’ infrared. All IR films come with an instruction sheet that suggests exposures, but they are rarely correct.

Most modern light meters incorporate sensors that are great for visible white light but can be ‘blind’ to infrared. Trying to estimate exposure from taking a white light reading and assuming it works with an infrared exposure is fraught with problems. Infrared is not necessarily proportionate to infrared.

Fortunately, old (and usually unwanted) light meter technology is sensitive to infrared radiation. Light meters like the Gossen 6 or Lunapro have sensors that detect infrared. By placing an IR filter over the sensor, thus eliminating all visible light entering the meter, you will see the needle deflect as it senses infrared. With experimentation, you can determine an ISO/ASA setting on the light meter, so the shutter speed/f-stop combination is accurate for a proper exposure in infrared. Using this technique, remember that the ISO/ASA you find is rarely the ISO setting the manufacturer recommends. Once you have calibrated your light meter to read reflected infrared, it should give you consistent results.

It is unfortunate that no manufacturer makes infrared film that is sensitive to wavelengths beyond about 820 nanometres, but the results are still exciting. Some manufacturers make films that only go to about 720 nanometres. They call it ‘infrared’ but I would argue it is barely extended red.

If you want to explore infrared beyond what any film can record, digital is, fortunately or unfortunately, your best option. 

[1] In 2007, Kodak discontinued Infrared HIE that was sensitive up to 900 nanometres. Since then, infrared films are only sensitive only up to about 750 nanometres.

[2] Colour infrared is a manufacturers creation and not a direct function of infrared radiation. This is why it was referred to as ‘false colour’ infrared.

[3] Maco films.

[4] Rollei infrared film.

Gale Spring & Danielle Edwards will be teaching a Workshop: Infrared from capture to print, at Gold Street Studios March 10 & 11 2023.

Danielle Edwards The Photograph Considered can be seen here.